Merrillite is a calcium phosphate mineral with the chemical formula Ca9NaMg(PO4)7. It is an anhydrous, sodium-rich member of the merrillite group of minerals.[4][5]
| Merrillite | |
|---|---|
| General | |
| Category | Phosphate mineral |
| Formula (repeating unit) | Ca9NaMg(PO4)7 |
| IMA symbol | Mer[1] |
| Strunz classification | 8.AC.45 |
| Crystal system | Trigonal |
| Crystal class | Ditrigonal pyramidal (3m) (same H-M symbol) |
| Space group | R3c |
| Unit cell | a = 10.362 Å, c = 37.106 Å; Z = 6 |
| Identification | |
| Color | Colorless to white |
| Crystal habit | Occurs as anhedral grains |
| Cleavage | Poor - indistinct |
| Tenacity | Brittle |
| Luster | Vitreous |
| Specific gravity | 3.1 (measured) |
| Optical properties | Uniaxial (-) |
| Refractive index | nε=1.62, nω=1.623 |
| Birefringence | 0.0030 |
| References | [2][3][4] |
Mineral species, sub-group and group
editMerrillite is a distinct mineral species but it also gives its name to a set of similar minerals, which together form the merrillite sub-group of minerals. The merrillite sub-group and the whitlockite sub-group together form the merrillite group of minerals.[6]
- Merrillite Group[6]
- Merrillite Sub-group
- Ferromerrillite
- Keplerite
- Matyhite
- Merrillite
- Whitlockite Sub-group
- Merrillite Sub-group
In September 2022 the discovery of another merrillite group mineral, changesite–(Y), was announced,[7] but, as of September 2022[update], it is not yet clear where this new mineral sits in the merrillite group hierarchy.
Discovery and naming
editMerrillite is named after George P. Merrill (1854–1929) of the Smithsonian Institution.[4] In 1915, Merrill had described the mineral from four meteorites: Alfianello, Dhurmsala, Pultusk and Rich Mountain. However, it was not until 1975 that it was recognized as distinct from whitlockite by the International Mineralogical Association.[4]
Occurrence
editMerrillite is a very important constituent of extraterrestrial rocks.[citation needed] It occurs in lunar rocks and in meteorites (for example, pallasites and martian meteorites).[8]
In 2022, for the first time, merrillite was found in a terrestrial environment, as an inclusion in lower-mantle diamonds from Sorriso River, Juína, Brazil.[9]
References
edit- ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
- ^ Mineralienatlas
- ^ Merrillite data on Webmineral
- ^ a b c d "Merrillite". Mindat. Retrieved 6 January 2013.
- ^ "Merrillite". Mindat. Retrieved 13 September 2022.
- ^ a b "Cerite Supergroup". Mindat. Retrieved 13 September 2022.
- ^ "New mineral found by Chinese scientists". China Daily. Retrieved 13 September 2022.
- ^ Jolliff, Bradley L.; John M. Hughes; John J. Freeman & Ryan A. Zeigler (2006). "Crystal chemistry of lunar merrillite and comparison to other meteoritic and planetary suites of whitlockite and merrillite". American Mineralogist. 91 (10): 1583–1595. Bibcode:2006AmMin..91.1583J. doi:10.2138/am.2006.2185. S2CID 140580667.
- ^ Kaminsky, Felix V.; Zedgenizov, Dmitry A. (2022). "First find of merrillite, Ca3(PO4)2, in a terrestrial environment as an inclusion in lower-mantle diamond". American Mineralogist. 107 (8): 1652–1655. doi:10.2138/am-2022-8175. S2CID 251071674.
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